Chemistry: Post your doubts here!

[Beaconite007]

Asalam Alaikum
Could somebody please solve Q1)a)ii of this paper.
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_4.pdf
In the markscheme, the answer is -0.59 but I keep getting +0.59
It also says in the markscheme to ignore the sign (so either answers are correct), but I'd just like to make sure what I'm doing wrong.

 

[Suchal Riaz]

today in my titration i got Ar of M in M2CO3 as 27.50 as M is group 1 metal i dont find any suitable metal with Ar of 27.50 should i write Na-23 as the answer as it is closest? or is my titration wrong. i got best titres 0.1cm3 apart so they seemed reliables. rough titre was 33.5cm, three titres were 32.00, 31.70, 31.80 so 31.75 seems correct to me. or maybe the laboratory guy mixed F1 and f3 in slightly wrong concentration. my working were quite good. My first time experience with As level experiment. what you think?
s2013/33

 

[AbbbbY]

today in my titration i got Ar of M in M2CO3 as 27.50 as M is group 1 metal i dont find any suitable metal with Ar of 27.50 should i write Na-23 as the answer as it is closest? or is my titration wrong. i got best titres 0.1cm3 apart so they seemed reliables. rough titre was 33.5cm, three titres were 32.00, 31.70, 31.80 so 31.75 seems correct to me. or maybe the laboratory guy mixed F1 and f3 in slightly wrong concentration. my working were quite good. My first time experience with As level experiment. what you think?
s2013/33

Close enough. I'd go with Na.

 

[AbbbbY]

today in my titration i got Ar of M in M2CO3 as 27.50 as M is group 1 metal i dont find any suitable metal with Ar of 27.50 should i write Na-23 as the answer as it is closest? or is my titration wrong. i got best titres 0.1cm3 apart so they seemed reliables. rough titre was 33.5cm, three titres were 32.00, 31.70, 31.80 so 31.75 seems correct to me. or maybe the laboratory guy mixed F1 and f3 in slightly wrong concentration. my working were quite good. My first time experience with As level experiment. what you think?
s2013/33

Close enough. I'd go with Na.

 

[punky21]

Hi I'm new here,
Could someone help me please?
9701/1/O/N/02

35. the element astatine lies below iodine in Group VII of the periodic table.
What will be the properties of astatine?

1 It forms diatomic molecules which dissociate more readily than chlorine molecules
2 It reacts explosively with hydrogen
3 It is a good reducing agent

Answer is 1 only, why is 3 incorrect?

39. Which ions are present in a solution of ethanol in an excess of concentrated sulphuric acid?

1 CH3CH2O^-
2 CH3CH2O^+H2
3 HSO4^-

Why is the answer 2 and 3?

Help is very much appreciated!

 

[Namehere]

Hi I'm new here,
Could someone help me please?
9701/1/O/N/02

35. the element astatine lies below iodine in Group VII of the periodic table.
What will be the properties of astatine?

1 It forms diatomic molecules which dissociate more readily than chlorine molecules
2 It reacts explosively with hydrogen
3 It is a good reducing agent

Answer is 1 only, why is 3 incorrect?

39. Which ions are present in a solution of ethanol in an excess of concentrated sulphuric acid?

1 CH3CH2O^-
2 CH3CH2O^+H2
3 HSO4^-

Why is the answer 2 and 3?

Help is very much appreciated!

For Q35 - 3 is incorrect because it is a "good" oxidising agent (Oxidising abilites of the halogens decrease as you go down the group). Astatine wants 1 more electron for it to be more stable therefore it needs to get reduced (OIL RIG - Reduction Is Gain of electrons), hence it is a good oxidising AGENT being itself reduced.

For Q39- 2 is correct because: The solution of sulphuric acid dissociates in the soltuion -> H2SO4 ----> HSO4- + H+ , then the ethanol, CH2CH3OH can accept a H+ from the dissociation of the Sulphuric acid to form the + ethanol ion, CH2CH3O+H2. Hence you have the HSO4- ion and the CH3CH2O+H2 ion present in the solution.
Just in case, the ethanol gains a + charge because it gains a proton (H+) and the H2SO4 gains a - charge because it lost a proton (H+)

Hope it helped.

 

[punky21]

Ohhh. Ok. It did. Thanks so much!

 

[Namehere]

Ohhh. Ok. It did. Thanks so much!

Np.

 

[Jaspreet Dhaliwal]

Can someone please help! my mocks are in about a weeks time :/
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Question 20
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Question 20
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Question 23
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Question 21
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Question 28
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf Question 23
would be appreciated if anyone could reply asap

 

[danial 234]

Q20
M/J 12 12
when this ester is hydrolysed, 2 products r formed. one is propanol and the other is sodium ethanoate.
Mr of propanol 60
Mr of sodium ethanoate 82
calculate %age
propanol 60/142*100= 42.3
Na ethanoate 82/142*100= 57.7

 

[danial 234]

Q 23
M/J 12 12
it is the addition of HBr to both cis trans isomers.
Answer is B.
in A , the 3rd compound is wrong. in it H2 is added rather than HBr.
in C, in 1st compound, Br2 is added.
in D, the first compound. in it carbon is forming 5 bonds. which cant happen
in B all compounds r corrct

 

[Kinki Tiffany 12]

http://studyguide.pk/Past Papers/CIE/International A And AS Level/9701 - Chemistry/9701_s02_qp_4.pdf

can anyone helps me with qns 1d?

 

[Jinosupreme]

Guys need some help.
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

Q 4, 5, 33, 35

4C (why only carboxylic acid BP affected by hydrogen bond, why not aldehyde too?)
5A
33A
35A

 

[danial 234]

Guys need some help.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf

Q 4, 5, 33, 35

4C (why only carboxylic acid BP affected by hydrogen bond, why not aldehyde too?)
5A
33A
35A

in 4) aldehyddes dont hv hydrogen bond. it hs one polar bond btween oxygen n carbon. hydrogen partial +ve ion is absent.
33) the compound hs similar structure to graphite. so all 3 r true

 

[danial 234]

5) the ideal gas law states that the gas molecules experience no forces of repulsion or attraction. HCl is opposite to this cz it is a large molecule n it has hydrogen bonding. so it is most likely to deviate. the remainig options only experience van der waals which is nt significant

 

[Jinosupreme]

Can anyone help me?
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf

Q18, 20, 33, 34, 35, 36

18C
20C
33D
34C
35D
36B

Really need help thanks :00

 

[danial 234]

18)) SO2 is acidic n will react with basic CaO. n will be neutralized.
33) statement 1 is ryt. statement 2 is wrong cz there is no triple bond btween Nitrogen. the third is also wrong cz the state of hydrazine doesnt affect.
34) MgCl2 conducts electricity in liwuid state also. while the remaining disassociate only in H20 n conduct electricity

 

[danial 234]

36) NH3 reduces Cl2. nd it is also a base. but the valency of H remains same.(+1)
35) Sr is just below the Ca .so hs almost same size. but both oxides r ionic n cn dissolve/ppt in H20. Hydroxyapatite doesnt contain metallic bond

 

[Namehere]

Can anyone help me?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf

Q18, 20, 33, 34, 35, 36

18C
20C
33D
34C
35D
36B

Really need help thanks :00

Q20- C -> A Nucleophilic addition reaction usually occurs when there is a C double bond, in this case at the second stage of the reaction the aldehyde (contains double bond) is joined with an oxygen, due to their difference in electronegativity a dipole is set up, leaving the carbon atom with a partial positive charge, allowing nucleophiles (negatively charged species, in this case ethanol due to the dipole in the O-H end) to be attracted to it.

Hope it helps.

 

[KZW]

Can anyone help me?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf

Q18, 20, 33, 34, 35, 36

18C
20C
33D
34C
35D
36B

Really need help thanks :00

18 ; CaO + SO2 -> CaSO3. You will need to learn it.

20 ; The aldehyde in the second reaction contains a partially positive carbon due to the oxygen bonded to it. The dipole set up makes it vulnerable to nucleophiles (The OH from ethanol).

33 ; Having high activation energy is fairly obvious. You probably got tripped up by 2. Hydrazine does not have a triple bonded nitrogen

34 ; All aqueous solutions will conduct. However, MgCl2 is an ionic solid. It conducts in a liquid state, so it should be excluded, hence only 2 and 3 are right.

35; Calcium hydroxide is less soluble than Strontium hydroxide due to the higher charge density, so 2 is eliminated. 3 should be eliminated, as it is fairly obvious why, and thus D is the only possible answer.

36; 2 is correct, as ammonia is a proton acceptor in this reaction. 1 is correct;8NH3 -> N2 + 6NH4. NH3 reduces itself to NH4, hence answer is B.

Hope it helps